Defined Benefit Pension Plans - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended		12 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Mar. 31, 2018
Defined Contribution Plan Disclosure [Line Items]
Contributions paid or to be paid by employer	$ 545	$ 417
Scenario, Forecast [Member]
Defined Contribution Plan Disclosure [Line Items]
Contributions paid or to be paid by employer			$ 1,031